Myocardial adaptation to ischemia by oxidative stress induced by endotoxin

Low-Dose Endotoxin Induces Late Preconditioning, Increases Peroxynitrite Formation, and Activates STAT3 in the Rat Heart

Administration of low-dose endotoxin (lipopolysaccharide, LPS) 24 h before a lethal ischemia induces pharmacological late preconditioning. The exact mechanism of this phenomenon is not clear. Here we aimed to investigate whether low-dose LPS exerts late effects on peroxynitrite formation and activation of Akt, Erk, and STAT3 in the heart. Male Wistar rats were injected with LPS (S. typhimurium; 0.5 mg/kg i.p.) or saline. Twenty-four hours later, hearts were isolated, perfused for 10 min, and then used for biochemical analyses. LPS pretreatment enhanced cardiac formation of the peroxynitrite marker 3-nitrotyrosine. LPS pretreatment also increased cardiac levels of the peroxynitrite precursor nitric oxide (NO) and superoxide. The activities of Ca²⁺-independent NO synthase and xanthine oxidoreductase increased in LPS-pretreated hearts. LPS pretreatment resulted in significantly enhanced phosphorylation of STAT3 and non-significantly increased phosphorylation of Akt without affecting the activation of Erk. In separate experiments, isolated working hearts were subjected to 30 min global ischemia and 20 min reperfusion. LPS pretreatment significantly improved ischemia-reperfusion-induced deterioration of cardiac function. We conclude that LPS pretreatment enhances cardiac peroxynitrite formation and activates STAT3 24 h later, which may contribute to LPS-induced late preconditioning.

Putative antioxidant property of sesame oil in an oxidative stress model of myocardial injury

BACKGROUND

Sesame oil is a potent antioxidant dietary source for human health. Oxidative stress through generation of free radicals damages the myocardium in different experimental condition. The present research was designed to evaluate the antioxidant property of chronic oral administration of sesame oil against isoproterenol induced myocardial injury.

METHODS AND RESULTS

Male Wistar albino rats were randomly divided into five groups (n = 6) and treated as per treatment protocol with two different doses of sesame oil (5 and 10 ml/kg b.w.) orally for thirty days. At the end of the treatment all the rats (except control rats) were administered with isoproterenol (85 mg/kg) two consecutive days and subjected to biochemical and histopathological estimation. Isoproterenol (group ISO) induced the oxidative myocardial damage via alteration in the endogenous antioxidant enzymes and myocardial marker enzymes. Sesame oil in both the dose (group S1 and S2) shows protective mechanism via decreasing thiobarbituric acid reactive substance (TBARS) and enhancing the endogenous antioxidant enzymes (reduced glutathione (GSH), superoxide dismutase (SOD) and Catalase). Sesame oil also increased the lactate dehydrogenase (LDH), creatine kinase (CK) and aspartate transaminase (AST) as a myocardial marker enzyme in heart homogenate. As histologically evident isoproterenol induced myocardial injury was well preserved by the chronic administration of sesame oil. The protective role of sesame oil was compared with the reference standard α-tocopherol (group S3) also showing the similar effect.

CONCLUSION

From this finding it has been concluded that chronic administration of sesame oil offers cardio protective action via putative antioxidant property.

Protective effect of propyl gallate against myocardial oxidative stress-induced injury in rat

This study was designed to investigate the effect of chronic administration of propyl gallate on myocardial oxidative stress-induced injury. Propyl gallate was administered orally to Wistar albino rats (150–200 g) in three different doses, by gastric gavage (250 mg kg−1 (P1), 500 mg kg−1 (P2) and 750 mg kg−1 (P3)), 6 days a week for 5 weeks. At the end of this period, all the rats, except the normal untreated rats that served as the control group, were administered isoproterenol (ISO), 85 mg kg−1 subcutaneously, for 2 consecutive days to induce myocardial injury. After 48 h, rats (n = 6 per group) were anaesthetized with anaesthetic ether, sacrificed and the hearts were harvested for the estimation of thiobarbituric acid reactive substances (TBARS), endogenous antioxidants (reduced glutathione (GSH), superoxide dismutase (SOD) and catalase) and for the assessment of histological changes. In the P2 BL group (BL = baseline), there was a significant (P < 0.001) rise in baseline TBARS and SOD when compared with the saline-treated group, while no such changes were observed in the other baseline-treated groups. However, there was a significant (P < 0.001) increase in TBARS and endogenous anti-oxidants (GSH, SOD and catalase) in the P2 ISO and P3 ISO groups, when the hearts were subjected to in-vivo myocardial oxidative stress-induced injury. We observed no such changes in the P1 ISO group. This study showed that propyl gallate modulates the levels of endogenous antioxidants present at the myocardial site. Whether these modifications are a result of direct interference at this site or a remote effect is not immediately clear. In conclusion, from the results it could be stated that chronic administration of 500 mg kg−1 of propyl gallate offers significant protection against myocardial oxidative stress-induced injury.

Cardioprotective effect of the Hibiscus rosa sinensis flowers in an oxidative stress model of myocardial ischemic reperfusion injury in rat

BACKGROUND

The present study investigates the cardioprotective effects of Hibiscus rosa sinensis in myocardial ischemic reperfusion injury, particularly in terms of its antioxidant effects.

METHODS

The medicinal values of the flowers of Hibiscus rosa sinensis (Chinese rose) have been mentioned in ancient literature as useful in disorders of the heart. Dried pulverized flower of Hibiscus rosa sinensis was administered orally to Wistar albino rats (150-200 gms) in three different doses [125, 250 and 500 mg/kg in 2% carboxy methyl cellulose (CMC)], 6 days per week for 4 weeks. Thereafter, rats were sacrificed; either for the determination of baseline changes in cardiac endogenous antioxidants [superoxide dismutase, reduced glutathione and catalase] or the hearts were subjected to isoproterenol induced myocardial necrosis.

RESULTS

There was significant increase in the baseline contents of thiobarbituric acid reactive substances (TBARS) [a measure of lipid per oxidation] with both doses of Hibiscus Rosa sinensis. In the 250 mg/kg treated group, there was significant increase in superoxide dismutase, reduced glutathione, and catalase levels but not in the 125 and 500 mg/kg treated groups. Significant rise in myocardial thiobarbituric acid reactive substances and loss of superoxide dismutase, catalase and reduced glutathione (suggestive of increased oxidative stress) occurred in the vehicle treated hearts subjected to in vivo myocardial ischemic reperfusion injury.

CONCLUSION

It may be concluded that flower of Hibiscus rosa sinensis (250 mg/kg) augments endogenous antioxidant compounds of rat heart and also prevents the myocardium from isoproterenol induced myocardial injury.

Cardioprotective effect of grape seed proanthocyanidins on isoproterenol-induced myocardial injury in rats

PURPOSE

To investigate whether grape seed proanthocyanidins (GSP) might protect the heart against myocardial injury (MI) induced by isoproterenol (ISO), in a rat model.

METHODS

GSP was administered orally to Wistar albino rats (150-180 g) in three different doses, by gastric gavage (50, 100 and 150 mg kg(-1) GSP), 6 days a week for 5 weeks. At the end of this period, all the rats, except the normal untreated rats that served as the control group, were administered ISO, 85 mg kg(-1) subcutaneously, for 2 consecutive days to induce myocardial injury. After 48 h, rats (n=6 per group) were anaesthetized with anesthetic ether, sacrificed and the levels of biochemical and histological observations of the heart tissues were performed.

RESULT

Our results suggest that prior administration of GSP maintained the levels of the marker enzymes (AST, ALT, LDH and CK) in all the treatment groups (GSP-50-ISO, GSP-100-ISO and GSP-150-ISO) when compared to ISO-injected rats. The entire baseline groups also showed no significant alterations in serum marker enzyme levels in comparison to that of control group. Interestingly, in this study, there was no significant change in the basal levels of myocardial TBARS, GST, SOD and CAT on administration of GSP in all the three dosages (GSP-50-BL, GSP-100-BL and GSP-150-BL). However, a significant decrease occurred in the levels of GSH and GPx in group GSP-50-BL, which in the absence of any cellular injury (as evidenced by histological studies), is considered to be non-lethal. In the ISO-injected group there was a significant rise in TBARS and a significant decrease in GSH, GPx, GST, SOD and CAT when compared to group control. The administration of GSP maintained the activities of these enzymes close to normal levels when compared to group ISO, which proves the stress stabilizing action of GSP. The biochemical and histological evidence from this study shows that 100 and 150 mg kg(-1) of GSP protected against ISO-induced myocardial injury.

CONCLUSION

This study demonstrates that GSP has a significant effect in the protection of heart against MI induced by ISO. We believe that pretreatment with GSP may contribute to developing novel strategies in the prevention and treatment of cardiotoxic effects of elevated levels of catecholamine.

2-D PAGE analysis of pesticide-induced stress proteins of E. coli

Logarithmically growing batch cultures of Escherichia coli were exposed to sublethal concentrations of pyrethroid and carbamate pesticides of four different technical grades. This induced 17-20 stress proteins, as observed using two-dimensional polyacrylamide gel electrophoresis. An E. coli culture growing exponentially in Luria Bertani medium (cell density approximately 2.3x10(9) cells/ml) was exposed to predetermined sublethal doses of individual pesticides. The cells were harvested after 30 minutes of induction and the stress response was developed in fresh LB medium for three hours under the same growth conditions. Cell pellets were obtained and stored in sonication buffer. Two-dimensional polyacrylamide gel electrophoresis was performed to resolve the proteins. Visualization of the protein spots by rapid silver staining showed 17-20 stress proteins which were absent in the standard protein profile of E. coli. On average 29% of these stress proteins were unique to the pollutant, while the remaining stress proteins overlapped with those of other pesticides. The iso-electric points (PIs) and molecular weights of the proteins were determined by comparing with protein markers with known PIs and molecular weights. Furthermore, upon comparing the pesticide-induced proteins within the same class and between the two different classes (pyrethroid and carbamate), it was apparent that the general nature of the stress remained the same throughout, which indirectly proved that the gene or set of genes responsible for stress expression are also the same, irrespective of the chemical nature of the substituents of the pesticides.

Preconditioning: Gender Effects1

Preconditioning is injury induced protection from subsequent injury. During preconditioning protective cellular responses to injury are up regulated resulting in acute and delayed defense against further damage. Several studies indicate that females experience a protective advantage after acute insult compared to males. Despite evidence of gender differences in acute injury, relatively few studies have evaluated whether there are sex differences in preconditioning. Variations in patients' pre-morbid preconditioning status may explain outcome variations that are not apparent in small animal studies. This review discusses the differences in response to acute injury experienced by males and females, the basic mechanisms of preconditioning, and the sex differences in the mechanisms of preconditioning.

Endotoxin increases ascorbate recycling and concentration in mouse liver

Sublethal exposure to Escherichia coli endotoxin [lipopolysaccharide (LPS)] attenuates the lethal effects of subsequent insults associated with oxidative stress, such as higher LPS dose, septic peritonitis, and ischemia. Because administration of the antioxidant ascorbate protects against these same insults and injection of dehydroascorbic acid (DHAA) protects against ischemia, the hypothesis that sublethal LPS increases endogenous ascorbate concentration and recycling (i.e., synthesis from DHAA) was tested. Injection of LPS [5 x 10(6) endotoxin units/kg body weight, i.p.] in mice caused a temporary inhibition of food intake, which was significant by 20 h and recovered within 3 d. LPS increased ascorbate concentration in adrenal gland, heart, kidney, and liver. LPS had similar effects in wild-type and Slc23a2+/- mice despite the latter's deficiency in the ascorbate transporter SVCT2. In liver, the ascorbate response to LPS was not accompanied by change in glutathione concentration. LPS decreased gulonolactone oxidase activity, which is rate-limiting for de novo synthesis of ascorbate from glucose, but increased the rate of DHAA reduction to ascorbate. In conclusion, sublethal endotoxin increases ascorbate recycling in liver and ascorbate concentration in liver, adrenal gland, heart, and kidney. The enhanced rate of ascorbate production from DHAA may protect these organs against the reactive oxygen species produced by subsequent, potentially lethal challenges.

Does endogenous testosterone mediate the lower preconditioning threshold in males?

BACKGROUND

Preconditioning is injury-induced protection from subsequent insult. Recent data indicates that males have lower preconditioning thresholds compared to females. Therefore, we hypothesized that testosterone may mediate the lower preconditioning threshold observed in males.

MATERIALS AND METHODS

Adult normal and castrated male Sprague-Dawley rats (n = 4-5) were given intraperitoneal (i.p.) injections of 125 or 500 microg/kg Salmonella typhimurium lipopolysaccharide (ETX) or 0.4 ml normal saline (NS). Another i.p. injection of 500 microg/kg ETX (injury dose) was given 24 h later. After 6 h, myocardial function was evaluated via the Langendorff perfusion model. Shams received only NS, while non-preconditioned rats (PC-) received NS followed by the 500 microg/kg ETX injury dose. Preconditioned rats received injections of 125 mug/kg ETX (PC +125) or 500 microg/kg ETX (PC +500), followed by the 500 microg/kg ETX injury dose.

RESULTS

Normal PC +125 and PC +500 males were preconditioned and maintained cardiac function similar to shams (P > 0.05). Castrated PC +125 and PC +500 males were also preconditioned and maintained cardiac function similar to castrated shams (P > 0.05). Conversely, both normal and castrated PC-males showed significantly decreased cardiac function compared to shams (P < 0.05).

CONCLUSIONS

Endogenous testosterone does not mediate the lower preconditioning threshold in males.

Is the Preconditioning Threshold Different in Females?

BACKGROUND

Preconditioning is injury induced protection against subsequent insult. Studies have shown that both males and females may be preconditioned. Females appear to have an innate cardioprotection, therefore, we hypothesized that the preconditioning threshold may differ between males and females.

MATERIALS AND METHODS

Male and female rats were divided into five groups (n=4-9). Animals were given an intraperitoneal (i.p.) injection of 125, 250, or 500 micrograms/kilogram Salmonella typhimurium lipopolysaccharide (ETX) or 0.4-ml normal saline (NS). After 24-h incubation another i.p. injection of either 500 micrograms/kilogram ETX (injury dose) or NS was given and the animals incubated an additional 6 h. Shams received two injections of NS. Non-preconditioned rats (PC-) received NS followed by ETX. Preconditioned rats had i.p. injections of 125 mug/kg ETX (PC +125), 250 microg/kg ETX (PC +250), or 500 microg/kg ETX (PC +500) followed by the injury dose ETX. The rats were then anesthetized and myocardial function evaluated with the Langendorff perfusion model.

RESULTS

PC +500 females were preconditioned and were able to maintain cardiac function similar to shams. Conversely, PC +125 females were not preconditioned with this stimulus and had a significant decrease in cardiac function similar to PC- rats. Male PC +500 and PC +125 rats, however, retained cardiac function comparable to shams, while PC- males showed a significant decrement.

CONCLUSIONS

Males and females may each be preconditioned by endotoxin; however, the preconditioning threshold is higher in females than males.

Preconditioning: evolution of basic mechanisms to potential therapeutic strategies

Preconditioning describes the phenomenon by which a traumatic or stressful stimulus confers protection against subsequent injury. Originally recognized in dog heart subjected to ischemic challenges, preconditioning has been demonstrated in multiple species, can be induced by various stimuli, and is applicable in different organ systems. Tremendous progress has been made elucidating the signal transduction cascade of preconditioning. Preconditioning represents a potent tissue-protective condition, and mechanistic understanding may allow safe clinical application. This review recalls the history of preconditioning and how it relates to the history of the investigation of endogenous adaptation; summarizes the current mechanistic understanding of acute preconditioning; outlines the signal transduction cascade leading to the development of delayed preconditioning; discusses preconditioning in noncardiac tissue; and explores the potential of using preconditioning clinically.

Reactive oxygen species as mediators of signal transduction in ischemic preconditioning

Ischemic preconditioning (IPC) is a most powerful endogenous mechanism for myocardial protection against ischemia/reperfusion injury. It is now apparent that reactive oxygen species (ROS) generated in the mitochondrial respiratory chain act as a trigger of IPC. ROS mediate signal transduction in the early phase of IPC through the posttranslational modification of redox-sensitive proteins. ROS-mediated activation of Src tyrosine kinases serves a scaffold for interaction of proteins recruited by G protein-coupled receptors and growth factor receptors that is necessary for amplification of cardioprotective signal transduction. Protein kinase C (PKC) plays a central role in this signaling cascade. A crucial target of PKC is the mitochondrial ATP-sensitive potassium channel, which acts as a trigger and a mediator of IPC. Mitogen-activated protein (MAP) kinases (extracellular signal-regulated kinase, p38 MAP kinase, and c-Jun NH(2)-terminal kinase) are thought to exist downstream of the Src-PKC signaling module, although the role of MAP kinases in IPC remains undetermined. The late phase of IPC is mediated by cardioprotective gene expression. This mechanism involves redox-sensitive activation of transcription factors through PKC and tyrosine kinase signal transduction pathways that are in common with the early phase of IPC. The effector proteins then act against myocardial necrosis and stunning presumably through alleviation of oxidative stress and Ca(2+) overload. Elucidation of IPC-mediated complex signaling processes will help in the development of more effective pharmacological approaches for prevention of myocardial ischemia/reperfusion injury.

Preconditioning potentiates redox signaling and converts death signal into survival signal

Reactive oxygen species (ROS) play a crucial role in the pathophysiology of ischemic heart disease by causing cardiac dysfunction and cell death. Several redox-sensitive anti- and pro-apoptotic transcription factors including NFkappaB and AP-1 progressively and steadily increase in the heart as a function of the duration of ischemia and reperfusion. When the heart is preconditioned to ischemic stress by repeated short-term ischemia and reperfusion, NFkappaB remains high while AP-1 is lowered to almost baseline value. The anti-apoptotic gene Bcl-2 is downregulated in the ischemic/reperfused heart, while it is upregulated in the adapted myocardium. Cardioprotective abilities of the preconditioning are abolished when heart is pre-perfused with N-acetyl cysteine, a scavenger for ROS, suggesting the role of ROS in redox signaling. Mammalian heart is protected by several defense systems which include among others, redox-regulated protein, thioredoxin. Reperfusion of ischemic myocardium results in the downregulation of thioredoxin 1 (Trx 1) expression, which was upregulated in the preconditioned myocardium. The increased expression of Trx 1 is completely blocked with an inhibitor of Trx 1, CDDP, which also abolished cardioprotection afforded by ischemic adaptation. The cardioprotective role of Trx 1 is confirmed further with transgenic mouse hearts overexpressing Trx 1. The Trx 1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size and apoptosis as compared to the corresponding wild-type mouse hearts. Taken together, preconditioning appears to potentiate redox signaling, which converts the "death signal" into "survival signal."

Endotoxin increases hepatic susceptibility to lipid peroxidation: A possible role of iron

The purpose of this study was to investigate the possible mechanism by which endotoxin enhances peroxidative damage to membrane lipids. Male B6C3 mice were treated with endotoxin intraperitoneally 0 or 20 mg/kg body weight for 24 h. Freshly prepared liver homogenate was incubated with either 1-5 mM of reduced glutathione (GSH), glucose, H(2)O(2), ascorbic acid (AA), FeSO(4), FeCl(3), EDTA, FeCl(3) plus AA, AA plus EDTA or EDTA plus FeCl(3) in phosphate-buffered saline (PBS), pH 7.0, or PBS, at 37 degrees C for 60 min. The levels of lipid peroxidation products, thiobarbituric acid reactants (TBAR), were significantly higher in the liver of endotoxin-treated mice, and the values were markedly increased following incubation. Compared to PBS, incubation with H(2)O(2), FeCl(3), FeSO(4), and AA, but not glucose, significantly enhanced TBAR formation. The greatest increase of TBAR was found when AA and FeCl(3) were added together. On the other hand, EDTA and GSH inhibited the formation of TBAR during incubation. When added before AA, EDTA completely inhibited the peroxidative effect of AA or FeSO4, and when added subsequent to AA, EDTA partially prevented the adverse effect of AA. The results obtained suggest that ionic iron plays an important role in initiating endotoxin-induced peroxidative damage to membrane lipids, and that AA may be involved in releasing iron from its protein complex and/or maintaining ionic iron in a reduced or catalytic state.

Cardioprotective effect of the alcoholic extract of Terminalia arjuna bark in an in vivo model of myocardial ischemic reperfusion injury

The present study was designed to investigate the effects of chronic administration of the alcoholic extract of Terminalia arjuna (TAAE) bark on isoproterenol induced myocardial injury. The TAAE was administered orally to Wistar albino rats (150-200 g) in three different doses, by gastric gavage [3.4 mg/kg: (T1), 6.75 mg/kg: (T2) and 9.75 mg/kg: (T3)] 6 days/week for 4 weeks. At the end of this period, all the animals, except the normal untreated rats that served as the control group, were administered isoproterenol (ISO) 85 mg/kg, S.C., for two consecutive days to induce in vivo myocardial injury. After 48 hours rats were anaesthetized with anaesthetic ether, then sacrificed and the hearts were harvested for biochemical and histological studies. A significant rise in myocardial thiobarbituric acid reactive substances (TBARS) and loss of reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (suggestive of increased oxidative stress) occurred in the hearts subjected to in vivo myocardial ischemic reperfusion injury. The 6.75 mg/kg TAAE treatment group (baseline) shows a significant increase in myocardial TBARS as well as endogenous antioxidants (GSH, SOD, and catalase), but not in the other treatment groups. In in vivo ischemic reperfusion injury of the TAAE treated rats there was a significant decrease in TBARS in all the groups. In 6.75 mg/kg treatment group, a significant rise in the levels of GSH, SOD and catalase were observed, and it shows better recovery profile than the other groups subjected to in vivo ischemic reperfusion injury. In histological studies, all the groups, except the isoproterenol treated group, showed preserved myocardium. The present study demonstrates that the 6.75 mg/kg TAAE augments endogenous antioxidant compounds of the rat heart and also prevents the myocardium from isoproterenol induced myocardial ischemic reperfusion injury.

Inhibition of oxygen radical formation by methylene blue, aspirin, or alpha-lipoic acid, prevents bacterial-lipopolysaccharide-induced fever

Phagocytic cells contain NADPH oxidase that they use for host defense by catalyzing the production of superoxide. Bacterial lipopolysaccharide (LPS) has been found to stimulate NADPH oxidase in mobile and sessile macrophages and microglia. It also evokes fever in homeothermic animals and men, a reaction mediated by central nervous system (CNS) activities. The purpose of the present study was to determine whether reactive oxygen species are involved in LPS-induced fever. In rabbits we found that plasma hydroperoxide levels increased and catalase activity decreased 15 min after LPS injection and that fever started with a similar latency, while plasma levels of tumor necrosis factor-alpha (TNFalpha) increased 30 min after the injection. Treating rabbits with methylene blue or aspirin did not affect TNFalpha secretion but prevented the LPS-induced rise of hydroperoxides and the inactivation of catalase, abolishing fever. Incubation of human blood with nitroblue tetrazolium and LPS increased the number of formazan-positive neutrophils from 10 +/- 5 to 52 +/- 9%. Adding LPS to blood preincubated with either methylene blue, alpha-lipoic acid, or aspirin respectively decreased the number of formazan-positive neutrophils to 0.9 +/- 0.8, 0.8 +/- 0.9, or 2.0 +/- 0.9%, disclosing the antioxidant capacity of these drugs. Systemic application of 80 mg/kg alpha-lipoic acid elicited heat-loss reactions within 15 min and decreased core temperature by 2.2 +/- 0.3 degrees C within 2 h. Alpha-lipoic acid applied 45 min after LPS induced antipyresis within 15 min, and this antipyresis was associated with a decrease of elevated hydroperoxide levels and restoration of catalase activity. Our results show that fever is prevented when the production of reactive oxygen species is blocked and that an elevated body temperature returns to normal when oxygen radical production decreases. Estimation of plasma dihydrolipoic acid (DHLA) levels following injection of 80 mg/kg alpha-lipoic acid in afebrile and febrile rabbits revealed that this acid is converted into DHLA, which in afebrile rabbits increased the plasma DHLA concentration from 2.22 +/- 0.26 microg/ml to peak values of 8.60 +/- 2.28 microg/ml DHLA within 30 min and which in febrile rabbits increased it from 0.84 +/- 0.22 microg/ml to peak values of 3.90 +/- 0.94 microg/ml within 15 min. Methylene blue, aspirin, and alpha-lipoic acid, which all cross the blood-brain barrier, seem to act not only on peripheral tissues but also on the CNS. Brain structures that have been shown to sense oxidative stress are vicinal thiol groups attached to the NMDA subtype of glutamate receptor. Their reduction by thiol-reducing drugs like dithiothreitol or DHLA has been found to increase glutamate-mediated neuronal excitability, while the opposite effect has been observed after their oxidation. Because we found that systemic application of alpha-lipoic acid in the afebrile state elicits hypothermia and in the febrile state is antipyretic, we think this type of NMDA receptor is involved in thermoregulation and that oxidation of its thiol groups induces fever. It appears that temperature homeostasis can be maintained only if the redox homeostasis of the brain is guaranteed.

Sublethal endotoxin administration evokes super-resistance to systemic hypoxia in rats

BACKGROUND

Systemic hypoxia following surgical injury modulates cytokine and catecholamine responses. Endotoxin tolerance develops after pretreatment of animals with sublethal endotoxin doses and is characterized by a reduced inflammatory cytokine response to subsequent endotoxin challenges. The administration of endotoxin also attenuates ischemic injury of rat myocardial tissue following hypoxia, a phenomenon described as cross-tolerance. The objectives of this study were: 1) to determine whether endotoxin evokes a cross-tolerance to systemic hypoxia in rats; and 2) to estimate circulatory and pulmonary performance in rats with systemic hypoxia after endotoxin pretreatment.

METHODS

Seventy-two hours before the experiment, Wistar rats were given an intraperitoneal injection of endotoxin at a dose of 10 microg/kg. Polyethylene catheters were inserted into the femoral vein for infusion, and into the femoral artery for blood sampling and blood pressure monitoring. Systemic hypoxia was achieved by continuous inhalation of a modified gas mixture (9% oxygen+ 91% N2) for 4 hours. Plasma TNF-alpha and IL-6 were measured by ELISA, and norepinephrine (NE) by HPLC.

RESULTS

The hypoxic rats that were pretreated with saline showed a significant decrease in mean arterial blood and base excess, as compared with the normoxic rats. Endotoxin pretreatment prevented the drop in mean arterial pressure during hypoxia and reduced the decrease in base excess. Hypoxic conditions markedly stimulated TNF-alpha and IL-6 release and increased NE levels, compared to the normoxic rats. Pretreatment with endotoxin suppressed the hypoxia-induced cytokine production as well as attenuating the increase in NE levels

CONCLUSIONS

In this rat hypoxia model, endotoxin pretreatment ameliorated the hypoxia-induced inflammatory response as well as suppressing the effects on arterial oxygenation, anaerobic metabolism and NE stimulation.

Repeated physiologic stresses provide persistent cardioprotection against ischemia-reperfusion injury in rats

OBJECTIVES

We investigated the time course of myocardial tolerance to ischemia-reperfusion injury after repeated physiologic or pharmacologic stresses.

BACKGROUND

Sublethal stress provides cardiac tolerance to ischemia-reperfusion injury and increases the activity of manganese superoxide dismutase (Mn-SOD) in the myocardium in a biphasic manner. However, few studies have investigated the time course of the cardioprotective effects after repeated stresses.

METHODS

One or two episodes of the same physiologic or pharmacologic stress (exercise, whole-body hyperthermia, or tumor necrosis factor-alpha treatment), or a combination of two different types of stress, were induced after a 48-h interval. The rats were then subjected to 20 min of left coronary artery occlusion, followed by 48 h of reperfusion. The interval between the last stimulus and the induced ischemia was between 0.5 h and 168 h. The incidence of ventricular fibrillation during ischemia and the size of the myocardial infarct after reperfusion were then examined.

RESULTS

When two episodes of physiologic or pharmacologic stress were induced, the beneficial effects against ischemia-reperfusion injury were observed in a monophasic manner. These effects persisted for a period of 0.5 to 60 h. One episode of sublethal stress provoked the same beneficial effects, but in a biphasic manner. The increase in Mn-SOD activity in the cardiac tissue resembled the time course for cardioprotection against ischemia-reperfusion injury.

CONCLUSIONS

Two episodes of physiologic or pharmacologic stress can provide persistent cardioprotective effects against ischemia-reperfusion injury.

Chronic garlic administration protects rat heart against oxidative stress induced by ischemic reperfusion injury

BACKGROUND

Oxidative stress plays a major role in the biochemical and pathological changes associated with myocardial ischemic-reperfusion injury (IRI). The need to identify agents with a potential for preventing such damage has assumed great importance. Chronic oral administration of raw garlic has been previously reported to augment myocardial endogenous antioxidants. In the present study, the effect of chronic oral administration of raw garlic homogenate on oxidative stress induced by ischemic-reperfusion injury in isolated rat heart was investigated.

RESULTS

Raw garlic homogenate (125, 250 and 500 mg/kg once daily for 30 days) was administered orally in Wistar albino rats. Thereafter, hearts were isolated and subjected to IRI (9 min. of global ischemia, followed by 12 min of reperfusion; perfusion with K-H buffer solution; 37 degrees C, 60 mm Hg.). Significant myocyte injury and rise in myocardial TBARS along with reduction in myocardial SOD, catalase, GSH and GPx were observed following IRI. Depletion of myocardial endogenous antioxidants and rise in TBARS were significantly less in the garlic-treated rat hearts. Oxidative stress induced cellular damage as indicated by ultrastructural changes, like disruption of myofilament, Z-band architecture along with mitochondrial changes were significantly less.

CONCLUSIONS

The study strongly suggests that chronic garlic administration prevents oxidative stress and associated ultrastructural changes, induced by myocardial ischemic-reperfusion injury.

Contractile function of rat myocardium is less susceptible to hypoxia/reoxygenation after acute infarction

In this study we tested the hypothesis that induction of heat shock proteins (HSPs) and antioxidant enzymes is a compensatory mechanism, which preserves the contractility of the surviving myocardium after acute myocardial infarction. For this purpose, mechanical function of isolated rat papillary muscles was tested 15 h after experimental myocardial infarction and sham operation, respectively. Contractility of the preparations was compared to the expression of HSP25, HSP72, and glutathione peroxidase activity (GSH-Px) at normoxia and during hypoxia/reoxygenation. At normoxic conditions, rates of isometric contraction and, in particular, of relaxation were significantly higher after acute myocardial infarction than after sham operation. Improved relaxation rates were reflected in 2- to 3-fold higher heat shock protein levels in papillary muscles from rats with myocardial infarction compared to sham operated animals. During hypoxia/reoxygenation, the rates of contraction and relaxation were better preserved after myocardial infarction than after sham surgery. Recovery of relaxation rates during reoxygenation was associated with increased HSP25 levels and enhanced GSH-Px activity after myocardial infarction. In conclusion, heat shock proteins exert a beneficial effect on cardiac muscle relaxation after acute myocardial infarction. Enhanced heat shock protein expression and GSH-Px activity may protect the contractile function of the surviving myocardium against the damaging influence of hypoxia/reoxygenation during the early post-infarct period.

Heat shock proteins and cardiovascular pathophysiology

In the eukaryotic cell an intrinsic mechanism is present providing the ability to defend itself against external stressors from various sources. This defense mechanism probably evolved from the presence of a group of chaperones, playing a crucial role in governing proper protein assembly, folding, and transport. Upregulation of the synthesis of a number of these proteins upon environmental stress establishes a unique defense system to maintain cellular protein homeostasis and to ensure survival of the cell. In the cardiovascular system this enhanced protein synthesis leads to a transient but powerful increase in tolerance to such endangering situations as ischemia, hypoxia, oxidative injury, and endotoxemia. These so-called heat shock proteins interfere with several physiological processes within several cell organelles and, for proper functioning, are translocated to different compartments following stress-induced synthesis. In this review we describe the physiological role of heat shock proteins and discuss their protective potential against various stress agents in the cardiovascular system.

Redox regulation of cardiomyocyte survival and death

In this review, attempts were made to establish the role of reactive oxygen species as signaling molecules that regulate cardiomyocyte life and death during ischemia and reperfusion. Ischemia/reperfusion is a classical example because partial or mild ischemia can lead to simultaneous execution and repair of the cardiomyocytes, which is disrupted during severe ischemia leading to cell necrosis because of the lack of ATP. Apoptosis and repair processes are mediated by adaptive response in which oxygen free radicals function as typical signaling molecules through the activation of receptor tyrosine kinases, protein kinase C, and mitogen-activated protein kinases, as well as induction of redox-sensitive transcription factors and genes.

The late phase of preconditioning

Unlike the early phase of preconditioning (PC), which lasts 2 to 3 hours and protects against infarction but not against stunning, the late phase of PC lasts 3 to 4 days and protects against both infarction and stunning, suggesting that it may have greater clinical relevance. It is now clear that late PC is a polygenic phenomenon that requires the simultaneous activation of multiple stress-responsive genes. Chemical signals released by a sublethal ischemic stress (such as NO, reactive oxygen species, and adenosine) trigger a complex cascade of signaling events that includes the activation of protein kinase C, Src protein tyrosine kinases, and nuclear factor kappaB and culminates in increased synthesis of inducible NO synthase, cyclooxygenase-2, aldose reductase, Mn superoxide dismutase, and probably other cardioprotective proteins. An analogous sequence of events can be triggered by a variety of stimuli, such as heat stress, exercise, and cytokines. Thus, late PC appears to be a universal response of the heart to stress in general. Importantly, the cardioprotective effects of late PC can be reproduced pharmacologically with clinically relevant agents (eg, NO donors, adenosine receptor agonists, endotoxin derivatives, or opioid receptor agonists), suggesting that this phenomenon might be exploited for therapeutic purposes. The purpose of this review is to summarize current information regarding the pathophysiology and mechanism of late PC.

Delayed myocardial protection induced by endotoxin does not involve kinin B(1)-receptors

Endotoxin is known to confer a delayed protection against myocardial infarction. Lipopolysaccharide (LPS) treatment also induces the de novo synthesis of kinin B(1)-receptors that are not present in normal conditions. The aim of this study was to evaluate whether LPS-induced B(1)-receptors are implicated in the reduction of infarct size brought about by LPS. Rabbits were submitted to a 30-min coronary artery occlusion and 3-h reperfusion sequence. Six groups were studied: pretreated or not (control animals) with LPS (5 microgram kg(-1) i.v.) 24 h earlier and treated 15 min before and throughout ischaemia - reperfusion with either the B(1)-antagonist R-715 (1 mg kg(-1) h(-1)), the B(1)-agonist Sar-[D-Phe(8)]-des-Arg(9)-bradykinin (15 microgram kg(-1) h(-1)) or vehicle (saline). Infarct size and area at risk were assessed by differential staining and planimetric analysis. The presence of B(1)-receptors in LPS-pretreated animals was confirmed by a decrease in mean arterial pressure in response to B(1) stimulation. LPS-pretreatment significantly reduced infarct size (6.4+/-1.7%, of area at risk vs 24.1+/-2.5% in control animals, P<0.05). This protection was not modified by B(1)-receptor antagonism (7.4+/-2.2%, NS) or stimulation (5.2+/-1.2%, NS). Neither antagonist nor agonist modified infarct size in control animals. In conclusion, these data suggest that LPS-induced myocardial protection in the rabbit is not related to concomitant de novo B(1)-receptor induction.

Activities of conjugating and antioxidant enzymes following endotoxin exposure

Endotoxin exposure elicits various responses in mammals including the acute phase response that has been shown to cause changes in the activity of several forms of cytochrome P450s and other enzymes. Therefore, the hepatic conjugating enzyme, glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT), the antioxidant enzymes, glutathione peroxidase (GSHPx), catalase, and superoxide dismutase (SOD), as well as lipid peroxidation were investigated following the administration of endotoxin to male Sprague-Dawley rats (8 mg/kg body weight). Rats were euthanized at various times following endotoxin administration and the livers removed and processed to assess various enzyme activities. Glutathione S-transferase, UDPGT, and GSHPx activity showed statistically significant decreases after 24 hours and remained lower than controls for the duration of the study. Decreases in total SOD and catalase activities were seen at 24, 48, and 72 hours following endotoxin administration; however, only catalase activity showed statistically significant differences between control and treated samples at those time points, and total SOD activity showed a statistically significant decrease at 24 hours. No statistically significant changes were seen in the level of lipid peroxidation in the liver microsomes from endotoxin-treated animals. Changes in the conjugative enzymes and the free-radical scavenging enzymes following endotoxin exposure may alter the host's metabolism and response to free radicals.

Apoptotic cell death during ischemia/reperfusion and its attenuation by antioxidant therapy

Apoptosis is a form of programmed cell death that can be induced in susceptible cells by a wide variety of normal physiological stimuli as well as by deleterious environmental conditions and cytotoxic agents. The common inducers of apoptosis include oxygen free radicals/oxidative stress and Ca(2+) which are also implicated in the pathogenesis of myocardial ischemic reperfusion injury. To examine how free radicals are directly involved in apoptosis, rats were divided into three groups. The first group of rat hearts were perfused for 15 min with KHB buffer, the second group of rat hearts were perfused with superoxide dismutase plus catalase, and the hearts were subjected to 30 min of ischemia and 120 min of reperfusion. The third group of rat hearts, served as control which were subjected to 165 min of perfusion with KHB buffer (where n=6 rats in each group). At the end of each experiment, hearts were saved (at -70 degrees C) and analysed for apoptosis, DNA laddening and MDA production. During the reperfusion continuous cardiac pressure measurements were recorded in real time with a data acquisition and analysis system (CORDAT II, Triton Technologies). Direct measurements of heart rate, developed pressure and the first derivative of the developed pressure were recorded before the intervention and during the reperfusion. Coronary flow was measured by timed collection of coronary effluent. The results of our study revealed apoptotic cells after 120 min of reperfusion as demonstrated by the intense fluorescence of the immunostained digoxigeninlabeled genomic DNA when observed under fluroscence microscopy. Evaluation of DNA fragmentation showed increased ladders of DNA bands in the same reperfused hearts representing integer multiples of the internucleosomal DNA, about 180 bp. The presence of apoptotic cells and DNA fragmentation in the myocardium were abolished by preperfusing the hearts in the presence of SOD and catalase, which also reduced the oxidative stress as evidenced by the MDA production. In concert, myocardial function was significantly better when compared with the ischemic control. Taken together, these results clearly demonstrate that oxidative stress developed in the ischemic reperfused myocardium induces apoptosis and free radical scavengers can play a crucial role in apoptotic cell death associated with ischemia/reperfusion.

Endotoxin induces a dose-dependent myocardial cross-tolerance to ischemia-reperfusion injury

OBJECTIVE

To test whether or not endotoxin induces a dose-dependent reduction of myocardial contractile dysfunction after a standardized period of myocardial ischemia and reperfusion and whether nitric oxide is involved in this form of myocardial protection.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Twenty-five male Sprague-Dawley rats.

INTERVENTIONS

After anesthesia, the left carotid artery was cannulated under sterile conditions and animals were allowed to recover from surgery for 12 hrs. Sterile saline or increasing doses (2.5, 5, or 10 mg/kg body weight) of endotoxin (Escherichia coli O26:B6; Sigma, Mississauga, Ontario, Canada) were given intravenously (1 mL over 5 mins). In some rats, diaspirin-crosslinked hemoglobin (200 mg/kg) was infused 6 hrs and 60 min before endotoxin infusion (10 mg/kg). Hearts were rapidly excised for retrograde perfusion through the ascending aorta (Langendorff apparatus) 6 hrs later. After baseline data collection, hearts were subjected to global ischemia (30 mins, 37 degrees C [98.6 degrees F]), followed by 30 mins of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Physiologic variables were recorded 6 hrs after saline and endotoxin infusion. Baseline myocardial systolic contractility and diastolic compliance were assessed, respectively, by left ventricular developed pressure (LVDP) and left ventricular (LV) volume-preload relationships. After 30 min of reperfusion, LVDP recovery and left ventricular end-diastolic pressure were measured. Endotoxin induced LV systolic contractile depression, irrespective of the dose of endotoxin administered. LV diastolic dysfunction varied between different doses of endotoxin administered. On reperfusion, endotoxin produced a dose-dependent improvement of postischemic LVDP recovery: 30+/-6% in sham, 78+/-9% in 2.5 mg/kg, 93+/-8% in 5 mg/kg, and 107+/-10% in 10 mg/kg endotoxin heart. In rats treated with 10 mg/kg endotoxin, diaspirin-crosslinked hemoglobin pretreatment abrogated endotoxin-induced postischemic LVDP recovery improvement (105+/-10% vs. 43+/-7%, p = .01).

CONCLUSION

Sublethal doses of endotoxin induce in a dose-dependent manner a delayed form of myocardial protection against ischemia. Although free-cell hemoglobin solution abrogates this endotoxin-induced cross-tolerance, we propose that possible mechanisms involved in this form of myocardial protection include nitric oxide pathway activation.

Dietary coenzyme Q(10) supplement renders swine hearts resistant to ischemia-reperfusion injury

To examine whether nutritional supplementation of coenzyme Q(10) (CoQ(10)) can reduce myocardial ischemia-reperfusion injury, a group of swine was fed a regular diet supplemented with CoQ(10) (5 mg x kg(-1) x day(-1)) for 30 days. Another group of pigs that were fed a regular diet supplemented with placebo served as a control. After 30 days, isolated in situ pig hearts were prepared and hearts were perfused with a cardiopulmonary pump system. Each heart was subjected to 15 min of regional ischemia by snaring of the left anterior descending coronary artery, followed by 60 min of hypothermic cardioplegic global ischemia and 120 min of reperfusion. After the experiments were completed, myocardial infarct size was measured by triphenyltrazolium chloride staining methods. Postischemic left ventricular contractile function was better recovered in the CoQ(10) group than in the control group of pigs. CoQ(10)-fed pigs revealed less myocardial infarction and less creatine kinase release from the coronary effluent compared with control pigs. The experimental group also demonstrated a smaller amount of malonaldehyde in the coronary effluent and a higher content of the endogenous antioxidants ascorbate and thiol. Significant induction of the expression of ubiquitin mRNA was also found in the hearts of the CoQ(10)-fed group. The results of this study demonstrate that nutritional supplementation of CoQ(10) renders the hearts resistant to ischemia-reperfusion injury, probably by reducing the oxidative stress.

Transportation or noise is associated with tolerance to myocardial ischemia and reperfusion injury

Myocardial stress can result in myocellular phenotypic changes including enhanced activity of antioxidant enzyme systems. Accordingly, endogenous tissue antioxidant enzyme activity has been associated with resistance to cardiac ischemia and reperfusion injury. The present study was designed to determine if environmental perturbations could alter myocardial antioxidant enzyme (catalase) activity and function after ischemia. Isolated perfused rat hearts (Langendorff apparatus, 37 degrees C) were subjected to 20 min global ischemia (37 degrees C) and 40 min reperfusion. Rats studied immediately following shipment had increased myocardial catalase activity (1330 +/- 3.5 U/g, P < 0.05 vs quarantined control) and increased resistance to ischemia and reperfusion injury (end reperfusion developed pressure, DP 55 +/- 4.0 mm Hg, P < 0.05 vs quarantined control). However, control rats that were quarantined for 4 weeks exhibited a progressive decrease in catalase activity (760 +/- 10 U/g) for 3 weeks of quarantine. There was a concurrent decrease in resistance to myocardial ischemia and reperfusion injury (DP 40 +/- 3.6 mm Hg). Similarly, quarantined rats subjected to construction-related noise levels in excess of 90 dB (A scale) had increased myocardial catalase activity (1140 +/- 3.3 U/g, P < 0.05) and functional tolerance to ischemia and reperfusion (DP 66 +/- 3.3 mm Hg, P < 0.05). Finally, rats experiencing 90-dB noise levels for 2 days exhibited increased myocardial catalase activity (1125 +/- 30 U/g, P < 0.05) and myocardial ischemia and reperfusion injury tolerance (DP 62 +/- 1.7 mm Hg, P < 0.05). We conclude that variations in environmental conditions can relate to changes in antioxidant defense mechanisms and tolerance to myocardial ischemia and reperfusion injury in the rat.

Myocardial protection by protykin, a novel extract of trans-resveratrol and emodin

Protykin is an all-natural, high potency standardized extract of trans-resveratrol (20%) and emodin (10%) derived from the dried rhizome of Polygonum cuspidatum. Previous studies have demonstrated free radical scavenging and anti-inflammatory activities of resveratrol. Since free radicals play a crucial role in the pathogenesis of myocardial ischemia/reperfusion injury, we examined whether Protykin could preserve the heart during ischemic arrest. Sprague-Dawley rats were divided into two groups: experimental group was gavaged Protykin (100 mg/kg body wt) dissolved in corn oil for three weeks, while the control group was gavaged corn oil alone. After three weeks, rats were sacrificed, isolated hearts perfused via working mode, were made globally ischemic for 30 min followed by 2 h of reperfusion. Left ventricular functions were continuously monitored and malonaldehyde (MDA) (presumptive marker for oxidative stress) formation were estimated. At the end of each experiment, myocardial infarct size was measured by TTC staining method. Peroxyl radical scavenging activity of Protykin was determined by examining its ability to remove peroxyl radical generated by 2,2'-azobis (2-amidinopropane) dihydrochloride, while hydroxy radical scavenging activity was tested with its ability to reduce 7-OH*-coumarin-3-carboxylic acid. The results of our study demonstrated that the Protykin group provided cardioprotection as evidenced by improved post-ischemic left ventricular functions (dp, dp/dt(max)) and aortic flow as compared to control group. This was further supported by the reduced infarct size in the Protykin group. Formation of MDA was also reduced by Protykin treatment. In vitro studies demonstrated that Protykin possessed potent peroxyl and hydroxyl radical scavenging activities. The results of this study indicate that Protykin can provide cardioprotection, presumably by virtue of its potent free radical scavenging activity.

Protection by protein A of apoptotic cell death caused by anti-AIDS drug zidovudine

Zidovudine, the anti-AIDS drug, caused inhibition of mitogen-induced proliferation and perturbation of cell-cycle progression of cultured bone marrow cells of mice. There was significant hypoploidy observed in flow cytometric analysis of AZT-treated bone marrow cells. In apo-direct analysis, cells showed apoptosis in G0/G1 phase. In DNA gel analysis, characteristic laddering of apoptosis was observed in AZT-treated bone marrow cells. We demonstrated that, when the animals were pretreated with protein A (PA) of Staphylococcus aureus, the apoptotic changes could be prevented in bone marrow cells of AZT-treated animals. There is a significant (p < 0.05) increase in proliferation of bone marrow cells subjected to mitogen treatment in PA+AZT-treated animals, compared to only AZT-treated animals. However, cell-cycle phase distribution was not hampered and no laddering in DNA gel analysis was also observed in this group. In apo-direct analysis, PA treatment showed significant (p < 0.001) inhibition of AZT-induced apoptosis. These observations indicate that by using a suitable agent such as protein A the toxic side effects of AZT could be minimized.

Reactive oxygen species function as second messenger during ischemic preconditioning of heart

Ischemic preconditioning has been shown to trigger a signaling pathway by potentiating tyrosine kinase phosphorylation leading to the activation of p38 MAP kinase and MAPKAP kinase 2. Recently, the nuclear transcription factor, NFkappaB, was found to play a role in the signaling process. Since NFkappaB is a target of oxygen free radicals, we hypothesized that reactive oxygen species might play a role in the signaling process. To test this hypothesis, isolated rat hearts were perfused in the absence or presence of either dimethyl thiourea (DMTU), a OH* radical scavenger, or SN 50 peptide, a NFkappaB blocker. Hearts were then subjected to ischemic preconditioning by four repeated episodes of 5 min ischemia each followed by 10 min reperfusion. All hearts were then made globally ischemic for 30 min followed by 2 h of reperfusion. The results of our study demonstrated enhanced tyrosine kinase phosphorylation during ischemic preconditioning which was blocked by DMTU. DMTU also inhibited preconditioning mediated increased phosphorylation of p38 MAP kinase and MAPKAP kinase 2 activity. However, DMTU had no effect on the translocation and activation of protein kinase C (PKC) resulting from preconditioning. Preconditioning reduced myocardial infarct size as expected. This cardioprotective effect of preconditioning was abolished by both DMTU and SN 50. Preconditioning resulted in the nuclear translocation and activation of NFkappaB. Increased NFkappaB binding was blocked by both DMTU and SN 50. The results of this study demonstrate that reactive oxygen species play a crucial role in signal transduction mediated by preconditioning. This signaling process appears to be potentiated by tyrosine kinase phosphorylation resulting in the activation of p38 MAP kinase and MAPKAP kinase 2 leading to the activation of NFkappaB suggesting a role of oxygen free radicals as second messenger. Free radical signaling seems to be independent of PKC although PKC is activated during preconditioning process suggesting the role of two separate signaling pathways in ischemic preconditioning.

Pharmacologic enhancement of tolerance to ischemic cardiac stress using monophosphoryl lipid A. A comparison with antecedent ischemia

In comparison with ischemic preconditioning, MLA-mediated cardioprotection seems to show numerous common features. Like ischemia, MLA induces a first and second window (biphasic profile) of heightened tolerance to ischemia. As with delayed ischemic preconditioning, MLA protects against infarction, stunning, and arrhythmias associated with ischemia-reperfusion. In contrast with acute ischemic preconditioning, MLA reduces infarction and stunning. A role has been demonstrated for nitric oxide synthase and KATP channel activation in the mechanism of delayed preconditioning induced by ischemia and by MLA. Regarding acute preconditioning, kinase and KATP channel activation have been implicated as involved in the mechanism of ischemic preconditioning and also in MLA cardioprotection. Use of MLA or related compounds as cardioprotectants may represent a method for inducing acute tolerance to ischemia-reperfusion injury manifested as infarction or stunning, with the added benefit of a sustained delayed cardioprotective state being achieved.

Oxygen free radical signaling in ischemic preconditioning

This review will focus on the free radical signaling mechanism of preconditioning. The results from our laboratory as well as studies from other laboratories suggest that reactive oxygen species function as second messenger during myocardial adaptation to ischemia. This review provides evidence for the first time that tyrosine kinase and MAP kinases are the targets for reactive oxygen species generated in the preconditioned myocardium. The finding that p38 MAP kinase might be upstream of NF kappa B further supports our previous reports that MAPKAP kinase 2 could be the most likely link between the preconditioning and adaptation mediated by gene expression. p38 activation appears to be an important step in the translocation and activation of the nuclear transcription factor NF kappa B, which in turn may be involved in the induction of the expression of a variety of stress-inducible genes.

Ischemic preconditioning triggers tyrosine kinase signaling: a potential role for MAPKAP kinase 2

Myocardial adaptation to ischemia has been shown to activate protein tyrosine kinase, potentiating activation of phospholipase D, which leads to the stimulation of mitogen-activated protein (MAP) kinases and MAP kinase-activated protein (MAPKAP) kinase 2. The present study sought to further examine the signal transduction pathway for the MAPKAP kinase 2 activation during ischemic adaptation. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase, whereas SB-203580 was used to inhibit p38 MAP kinases. Western blot analysis demonstrated that p38 MAP kinase is phosphorylated during ischemic stress adaptation. Phosphorylation of p38 MAP kinase was blocked by genistein, suggesting that activation of p38 MAP kinase during ischemic adaptation is mediated by a tyrosine kinase signaling pathway. MAPKAP kinase 2 was estimated by following in vitro phosphorylation with recombinant human heat shock protein 27 as specific substrate for MAPKAP kinase 2. Again, both genistein and SB-203580 blocked the activation of MAPKAP kinase 2 during myocardial adaptation to ischemia. Immunofluorescence microscopy with anti-p38-antibody revealed that p38 MAP kinase is primarily localized in perinuclear regions. p38 MAP kinase moves to the nucleus after ischemic stress adaptation. After ischemia and reperfusion, cytoplasmic striations in the myocytes become obvious, indicating translocation of p38 MAP kinase from nucleus to cytoplasm. Corroborating these results, myocardial adaptation to ischemia improved the left ventricular functions and reduced myocardial infarction that were reversed by blocking either tyrosine kinase or p38 MAP kinase. These results demonstrate that myocardial adaptation to ischemia triggers a tyrosine kinase-regulated signaling pathway, leading to the translocation and activation of p38 MAP kinase and implicating a role for MAPKAP kinase 2.

Increased levels of myocardial IkappaB-alpha protein promote tolerance to endotoxin

Endotoxin [lipopolysaccharide (LPS)] causes tumor necrosis factor-alpha (TNF-alpha)-mediated myocardial contractile depression. Tolerance to the cardiac toxicity of LPS can be induced by a prior exposure to LPS or by pretreatment with glucocorticoids. The mechanisms by which the myocardium acquires tolerance to LPS remain unknown. LPS causes phosphorylation and degradation of inhibitory kappaB-alpha (IkappaB-alpha), releasing nuclear factor-kappaB (NF-kappaB) to activate TNF-alpha gene transcription. We hypothesized that LPS induces supranormal synthesis of myocardial IkappaB-alpha protein and thus renders the myocardium tolerant to subsequent LPS. Rats were challenged with LPS after pretreatment with LPS, dexamethasone, or saline. In saline-pretreated rats, LPS caused a rapid decrease in myocardial IkappaB-alpha protein levels, activation of NF-kappaB, and increased TNF-alpha production. These events were followed by myocardial contractile depression. After the initial decrease in myocardial IkappaB-alpha, IkappaB-alpha protein levels rebounded to a level greater than control levels by 24 h. Dexamethasone pretreatment similarly increased myocardial IkappaB-alpha protein levels. In rats pretreated with either LPS or dexamethasone, myocardial IkappaB-alpha protein levels remained similar to control levels after LPS challenge. The preserved level of myocardial IkappaB-alpha protein was associated with diminished NF-kappaB activation, attenuated myocardial TNF-alpha production, and improved cardiac contractility. We conclude that LPS and dexamethasone upregulate myocardial IkappaB-alpha protein expression and that an increased level of myocardial IkappaB-alpha protein may promote cardiac tolerance to LPS by inhibition of NF-kappaB intranuclear translocation and myocardial TNF-alpha production.

Myocardial gene reprogramming associated with a cardiac cross-resistant state induced by LPS preconditioning

Lipopolysaccharide (LPS) preconditioning induces cardiac resistance to subsequent LPS or ischemia. This study tested the hypothesis that resistance to LPS and resistance to ischemia are two manifestations of cardiac cross-resistance which may involve reprogramming of cardiac gene expression. Rats were preconditioned with a single dose of LPS (0.5 mg/kg ip). Cardiac resistance to LPS was examined with a subsequent LPS challenge. Cardiac resistance to ischemia was determined by subjecting hearts to ischemia-reperfusion. Total RNA was extracted from myocardium for Northern analysis of mRNAs encoding protooncoproteins, antioxidant enzymes, and contractile protein isoforms. Rats preconditioned with LPS 1-7 days earlier acquired cardiac resistance to endotoxemic depression. This resistance temporally correlated with resistance to ischemia. Pretreatment with cycloheximide (0.5 mg/kg ip) abolished resistance to both LPS and ischemia. LPS preconditioning induced the expression of c-jun and c-fos mRNAs. LPS also transiently increased mRNAs encoding catalase and Mn-containing superoxide dismutase. The expression of both alpha- and beta-myosin heavy chain mRNAs was upregulated, whereas the expression of cardiac alpha-actin mRNA was suppressed. We conclude that 1) LPS induces sustained cardiac resistance to both LPS and ischemia, 2) resistance to ischemia and resistance to LPS seem to be two mechanistically indistinct components of cardiac cross-resistance, and 3) the cardiac cross-resistance is associated with reprogramming of myocardial gene expression.

Heat stress pretreatment mitigates postischemic arachidonic acid accumulation in rat heart

Heat stress pretreatment of the heart is known to protect this organ against an ischemic/reperfusion insult 24 h later. Degradation of membrane phospholipids resulting in tissue accumulation of polyunsaturated fatty acids, such as arachidonic acid, is thought to play an important role in the multifactorial process of ischemia/reperfusion-induced damage. The present study was conducted to test the hypothesis that heat stress mitigates the postischemic accumulation of arachidonic acid in myocardial tissue, as a sign of enhanced membrane phospholipid degradation. The experiments were performed on hearts isolated from rats either 24 h after total body heat treatment (42 degrees C for 15 min) or 24 h after sham treatment (control). Hearts were made ischemic for 45 min and reperfused for another 45 min. Heat pretreatment resulted in a significant improvement of postischemic hemodynamic performance of the isolated rat hearts. The release of creatine kinase was reduced from 30 +/- 14 (control group) to 17 +/- 5 units/g wet wt per 45 min (heat-pretreated group) (p < or = 0.05). Moreover, the tissue content of the inducible heat stress protein HSP70 was found to be increased 3-fold 24 h after heat treatment. Preischemic tissue levels of arachidonic acid did not differ between heat-pretreated and control hearts. The postischemic ventricular content of arachidonic acid was found to be significantly reduced in heat-pretreated hearts compared to sham-treated controls (6.6 +/- 3.3. vs. 17.8 +/- 12.0 nmol/g wet wt). The findings suggest that mitigation of membrane phospholipid degradation is a potential mechanism of heat stress-mediated protection against the deleterious effects of ischemia and reperfusion on cardiac cells.

An essential role of NFkappaB in tyrosine kinase signaling of p38 MAP kinase regulation of myocardial adaptation to ischemia

We have recently demonstrated that myocardial adaptation to ischemia triggers a tyrosine kinase regulated signaling pathway leading to the translocation and activation of p38 MAP kinase and MAPKAP kinase 2. Since oxidative stress is developed during ischemic adaptation and since free radicals have recently been shown to function as an intracellular signaling agent leading to the activation of nuclear transcription factor, NFkappaB, we examined whether NFkappaB was involved in the ischemic adaptation process. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase while SB 203580 was used to inhibit p38 MAP kinases. Ischemic adaptation was associated with the nuclear translocation and activation of NFkappaB which was significantly blocked by both genistein and SB 203580. The ischemically adapted hearts were more resistant to ischemic reperfusion injury as evidenced by better function recovery and less tissue injury during post-ischemic reperfusion. Ischemic adaptation developed oxidative stress which was reflected by increased malonaldehyde formation. A synthetic peptide containing a cell membrane-permeable motif and nuclear sequence, SN 50, which blocked nuclear translocation of NFkappaB during ischemic adaptation, significantly inhibited the beneficial effects of adaptation on functional recovery and tissue injury. In concert, SN 50 reduced the oxidative stress developed in the adapted myocardium. These results demonstrate that p38 MAP kinase might be upstream of NFkappaB which plays a role in ischemic preconditioning of heart.

High-performance liquid chromatographic peak identification of 2,4-dinitrophenylhydrazine derivatives of lipid peroxidation aldehydes by photodiode array detection

Malonaldehyde (MDA), a product of lipid peroxidation, is a presumptive marker for the development of oxidative stress in tissues and plasmas. In this study we report the photodiode array detection of the 2,4-dinitrophenylhydrazine (DNPH) derivatives of MDA using HPLC. Oxidative stress was produced by injecting (i.p.) bacterial lipopolysaccharide (LPS) into rats at a dose of 100 micrograms/kg, or i.v. into rabbits (1 microgram/kg), or added to freshly drawn human blood (200 ng/ml). Blood was collected at several time points up to 5 h, centrifuged, and equal volumes of 20% TCA were used to precipitate proteins from the plasma. The supernatants were derivatized with DNPH, and the aldehyde-DNPHs were extracted with pentane. After evaporation, aliquots of 10 microliters in acetonitrile were injected onto a Beckman Ultrasphere C18 (3 microns) column, chromatographed with an acetonitrile-water-acetic acid gradient mobile phase and scanned using Waters 996 photodiode array detector. Peak identification and homogeneity was determined by comparing the experimental peaks and UV scans with those of authentic standards. A significant increase in the DNPH derivative of malonaldehyde (MDA-DNPH), but not of the other aldehyde-DNPH derivatives of formaldehyde (FDA), acetaldehyde (ADA), acetone and propionaldehyde (PDA) was seen over the first hour after LPS administration in anesthetized rats, while in conscious rabbits this trend lasted up to 3 h. The retention times as well as the UV scans of the derivatized aldehydes matched the authentic standards. Thus, photodiode array detection has proved valuable in establishing this HPLC method for estimating oxidative stress. This technique could accurately measure pmol amounts of MDA-DNPH indicating the usefulness of photodiode array detection method for estimating small changes in the oxidative stress.

Tumor necrosis factor in the heart

The heart is a tumor necrosis factor (TNF)-producing organ. Both myocardial macrophages and cardiac myocytes themselves synthesize TNF. Accumulating evidence indicates that myocardial TNF is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Indeed, locally (vs. systemically) produced TNF contributes to postischemic myocardial dysfunction via direct depression of contractility and induction of myocyte apoptosis. Lipopolysaccharide or ischemia-reperfusion activates myocardial P38 mitogen-activated protein (MAP) kinase and nuclear factor kappa B, which lead to TNF production. TNF depresses myocardial function by nitric oxide (NO)-dependent and NO-independent (sphingosine dependent) mechanisms. TNF activation of TNF receptor 1 or Fas may induce cardiac myocyte apoptosis. MAP kinases and TNF transcription factors are feasible targets for anti-TNF (i.e., cardioprotective) strategies. Endogenous anti-inflammatory ligands, which trigger the gp130 signaling cascade, heat shock proteins, and TNF-binding proteins, also control TNF production and activity. Thus modulation of TNF in cardiovascular disease represents a realistic goal for clinical medicine.

Exercise-induced stress response as an adaptive tolerance strategy

Interaction between the quality of the environment and the health of the exposed population determines the survival response of living organisms. The phenomenon of induced tolerance by exposure to threshold levels of stressors to stimulate natural defense mechanisms has potential therapeutic value. The paucity of information on predictability of individual response and information on the operative fundamental mechanisms limit applicability of the adaptive tolerance strategy. A potential biomarker of the stress response includes members of the stress-inducible ubiquitin gene family. Transcript sizes detected with Northern blot analysis identify different classes of ubiquitin gene family members and the intensity of the radioactive signal allows abundance determinations. Using moderate exercise as the stressor, significant increase (p < 0.028) in abundance of inducible polyubiquitin genes was found in human blood. Both the potential of exercise as a model system of a natural stress inducer and polyubiquitin as a biomarker of stress were established in these studies.

Redistribution of phosphatidylethanolamine and phosphatidylserine precedes reperfusion-induced apoptosis

Although cardiomyocyte death and infarction associated with ischemia-reperfusion are traditionally believed to be induced via necrosis, recent studies implicated apoptotic cell death in ischemic reperfused tissue. To examine whether myocardial ischemic reperfusion injury is mediated by apoptotic cell death, isolated perfused rat hearts were subjected to 15 and 30 min of ischemia as well as 15 min of ischemia followed by 30, 90, or 120 min of reperfusion. At the end of each experiment, hearts were processed for the evaluation of apoptosis and DNA laddering. Apoptosis was studied by visualizing the apoptotic cardiomyocytes by direct fluorescence detection of digoxigenin-labeled genomic DNA using APOPTAG in situ apoptosis detection kit. DNA laddering was evaluated by subjecting the DNA obtained from cardiomyocytes to 1.8% agarose gel electrophoresis and photographed under ultraviolet illumination. In addition, high-performance thin-layer chromatography (HPTLC) of aminophospholipids labeled with 2,4,6-trinitrobenzenesulfonate was performed to evaluate phospholipid topography in cardiomyocytes. The results of our study revealed apoptotic cells only in the 90- and 120-min reperfused hearts as demonstrated by the intense fluorescence of the immunostained digoxigenin-labeled genomic DNA when observed under fluorescence microscope. None of the ischemic hearts showed any evidence of apoptosis. These results corroborated with the findings of DNA fragmentation that showed increased ladders of DNA bands in the 120-min reperfused hearts, representing integer multiples of the internucleosomal DNA length (approximately 180 bp). Two-dimensional HPTLC of the phospholipids obtained from the cardiomyocytes and transbilayer organization of the phosphatidylethanolamine (PE) and phosphatidylserine (PS) in the myocytes indicated translocation of both PE and PS from the inner leaflet to the outer leaflet of the membrane as early as after 20 min of ischemia. These results demonstrate that the redistribution of PS and PE precedes the apototic cell death and DNA fragmentation associated with the reperfusion of ischemic myocardium, suggesting that ischemia may trigger the signal for apoptosis although it becomes evident during reperfusion.